#include <bits/stdc++.h>
using namespace std;

#define int int64_t
#define endl "\n"

using PII = pair<int, int>;
using TII = tuple<int, int, int>;
template<class T>
using V = vector<T>;
using i64 = long long;
using i128 = __int128;
using u64 = unsigned long long;

#define FOR(i, a, b) for (int i = (int)(a); i <= (int)(b); i++)
#define FOR2(i, a, b, c) for (int i = (int)(a); i <= (int)(b); i += c)
#define FORD(i, b, a) for (int i = (int)(a); i >= (int)(b); i--)
#define FORD2(i, b, a, c) for (int i = (int)(a); i >= (int)(b); i -= c)
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.rbegin(), a.rend()
#define lowbit(x) ((x)&(-x))
#define RE return;
#define Yes cout << "Yes" << endl;
#define YES cout << "YES" << endl;
#define No cout << "No" << endl;
#define NO cout << "NO" << endl;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define sz size()

void solve () {
    int n;
    cin >> n;

    struct E {
        int x, y, id;
    };

    V<E>a (n), b (n);

    FOR (i, 0, n - 1) cin >> a[i].x >> a[i].y, a[i].id = i + 1;

    sort (ALL (a), [&] (E c, E d) {
        return c.x < d.x;
    });

    sort (a.begin (), a.begin () + n / 2, [&] (E c, E d) {
        return c.y < d.y;
    });

    sort (a.begin () + n / 2, a.end (), [&] (E c, E d) {
        return c.y > d.y;
    });

    FOR (i, 0, n / 2 - 1)cout << a[i].id << ' ' << a[i + n / 2].id << endl;

}

signed main () {
    int Task = 1;

    ios::sync_with_stdio (false);
    cin.tie (nullptr);
    cin >> Task;

    while (Task--) {
        solve ();
    }

    return 0;
}